Introduction to Ketones

Ketones are a class of organic compounds containing a carbonyl group (C=O) bonded to two carbon atoms. Their general formula is R–CO–R', where R and R′ can be the same or different alkyl or aryl groups.

Key Characteristics

• Functional group: Carbonyl group (C=O) within the carbon chain.
• Position: Carbonyl carbon is bonded to two other carbon atoms (unlike aldehydes).
• Polarity: Ketones are polar due to the electronegative oxygen atom.
• Hydrogen bonding: Cannot form hydrogen bonds with themselves (only with water).

Structure of Ketones

The carbonyl carbon in ketones is sp² hybridized, making the structure planar around the carbonyl group. The angle between substituents is approximately 120°.

The carbon–oxygen double bond consists of a sigma (σ) bond and a pi (π) bond. The oxygen has a partial negative charge, making the carbon electrophilic.

Nomenclature of Ketones

• IUPAC Name: Based on the longest carbon chain containing the ketone group. Replace -e of alkane with -one.
• Examples:
  • CH₃–CO–CH₃ → Propan-2-one (Common name: Acetone)
  • CH₃–CO–C₂H₅ → Butan-2-one

Physical Properties of Ketones

• Moderate boiling points (higher than alkanes, lower than alcohols).
• Soluble in water (small ketones) due to hydrogen bonding with water molecules.
• Colorless liquids with a sweet or pungent odor.

Common Examples of Ketones

• Acetone: CH₃COCH₃ – used in nail polish remover.
• Butanone: CH₃COC₂H₅ – used as a solvent.
• Camphor: Natural ketone used in balms and vaporizers.

Quick MCQ Quiz on Ketones

1. What is the functional group of ketones?
   a) –OH
   b) –CHO
   c) –CO–
   d) –COOH
   Answer: c) –CO–
2. Which of the following is the simplest ketone?
   a) Methanol
   b) Acetone
   c) Ethanal
   d) Butanone
   Answer: b) Acetone
3. What is the hybridization of the carbonyl carbon in ketones?
   a) sp
   b) sp²
   c) sp³
   d) dsp²
   Answer: b) sp²
4. Which ketone is naturally found in camphor?
   a) Acetone
   b) Butanone
   c) Camphor
   d) Propanone
   Answer: c) Camphor
5. Ketones cannot form hydrogen bonds with:
   a) Water molecules
   b) Alcohols
   c) Themselves
   d) Amines
   Answer: c) Themselves

True or False

• Ketones have the general formula R–CO–R′. True ✅
• Ketones can hydrogen bond with themselves. False ❌ (They can only bond with water molecules)
• The carbonyl carbon in ketones is sp² hybridized. True ✅
• All ketones are insoluble in water. False ❌ (Small ketones are soluble)

Related Topics: Aldehydes, Alcohols
External Resource: Wikipedia – Ketones, NCERT Chemistry Class 12.